knuckleduster
noun [ C ] uk/ˈnʌk.əlˌdʌs.tər/ us/ˈnʌk.əlˌdʌs.tɚ/
UK (US brass knuckles)指节铜套（一种套在指节上以增加伤害力的武器）
a metal weapon that is worn over the knuckles and is intended to increase the injuries caused when hitting a person
informal大戒指
a large and noticeable ring